This API is mainly for Terminal Emulator implementors, or those writing programs
that expect to interpreted by a terminal emulator and wish to determine the
printable width of a string on a Terminal.

Usually, the length of the string is equivalent to the number of cells it
occupies except that there are are also some categories of characters which
occupy 2 or even 0 cells. POSIX-conforming systems provide wcwidth(3) and
wcswidth(3) of which this module's interface mirrors precisely.
